2002 Camry POOR MILEAGE

Automatic, 110k miles, well maintained, dealer yesterday verified O2 sensors
etc are all working, and could find nothing wrong with the vehicle. Checked

just about everything, including plugs, air filter, ad infinitum,
connections, PCV valve, etc, etc, etc., including brakes.
Poor mileage (17mpg) has been going on for about a month. Was at least
mid-20's before the drop.
I'm thinking: change the O2 sensor behind the catalytic, and see what that
does.
Totally at a loss here.

Why do you think this would make a difference?
It will your money, but little else.

If you're burning E10 (90% gasoline and 10 ethanol), that can cut your
mileage down by 3% or so, which would be around 0.75 mpg. Other stuff
added to the gasoline to cut down on smog might be hurting the mileage, too.
I can't help but wonder, now that summer is here, if your driving habits
have changed.
Make sure tires are filled with gas (air), too.
Jeff

Did you get new tires recently? Are you sure you were getting mid-20's
before the "drop"? According to the EPA, a 2002 4 cylinder automatic
Camry was rated 21/29. Mid-20's seems reasonable for mixed driving.
Any chance you have a brake dragging? After a long drive, feel the
wheel hubs (be careful) - if one is especially hot, suspect a dragging
brake. Any chance they changed the gas formulation in your area (where
are you)? Any changes in your driving pattern? Notice any changes in
the transmission behavior? Any chance you have a teenager? Or maybe
you park your car in a vulnerable area where someone can steal gas?
How good are your gas mileage records? Basing fuel mileage on a single
tank average can be very misleading. You need to compute an average
over 3 or more tank fulls.
If your check engine light is not on, it is unlikely the problem is
your engine. Do you smell "gas" when you first get out of your car or
when you are driving with the windows down? A leaking connection could
explain everything. Are you in a rust prone area? I've heard stories
of Camry tanks rusting out on top...could let some gas slosh out, but
you should smell this.

Waste of time and money. The sensor behind the catalyst is there to
verify the catalytic converter is working. It is not used to adjust
the fuel mixture.

For a 2002 car with OBDII it is very unlikely that any of these
potential problems would reduce the mileage by 39% without also
turning on the check engine light. My experience has been that even
minor, almost undetectable miss fires will turn on the CEL. A clogged
fuel filter is more likely to affect performance than fuel economy. I
suppose the timing could be off, but for a car without a distributor,
the only way the timing is off enough to reduce mileage by 30% is for
something major to have gone wrong, and the CEL should be on in this
case.
Ed

Many people ignore changing the fuel filter. I listed it more as a
reminder than a cure to poor gas mileage.
Are all the vacuum line in place? Even if they are in place, check
them for cracks.
Do you have a bad wheel bearing?
Are the fluid levels at the proper level in the transmission and
differential?
Is the transmission slipping?
Is the air filter dirty?
Are the spark plugs out of dirty or out of spec?
Is the correct oil in the engine?

Timing retards as the belt stretches and can cost 4mpg, it did to
me...old plugs, rotor cap wires can cost 1-2 mpg. change differential
and trans and motor to synthetic 5-30 mobil 1, check brakes and how
wheels spin on a lift, A bad 02 sensor, fuel leak, a bad battery
needing the alternator to work constantly adds load. Id start with
timing and oils

The OP's car has a timing chain instead of a belt so that is out as a
possible cause of poor fuel economy.
I believe that the 2002 Camry uses one coil per cylinder so it does not have
a distributor, cap, rotor, or high-tension wires.
The OP did not mention how many miles are on the current spark plugs, and if
they have over 60,000 miles on them, then they are worth checking.
I don't think the OP defined what he or she thought as "poor" mileage, but
changing differential, transmission, and motor oil to synthetic probably
will not make a discernable difference in fuel economy.
Dragging brakes can cause poor fuel economy, but there are generally other
symptoms that accompany dragging brakes, such as pulling or drifting, noise,
rapid brake lining wear, or pulsation from rotor or drum deformation.
In an OBD II compliant vehicle, an O2 sensor that is bad enough to cause a
discernable deterioration in fuel economy would probably also cause the
malfunction indicator light to come on.
A fuel leak is a possibility, but I have not seen one in any late-model
Toyotas.
If I were checking a car for poor fuel economy, I would make sure that the
car is up-to-date with periodic maintenance, including air filter and spark
plugs, check manifold vacuum, check for proper tire inflation, check for
dragging wheels, check the condition of the ATF, and go for a ride with the
customer to get an idea of driving conditions and driving habits.

According to the faq section at Toyota's web site, the 4 cylinder engine in
the 2002 Camry has a timing chain. go to www.toyota.com, and under the
"About Toyota" tab, click on "Search/Help." On the Help/Search page, click
on the "Frequently Asked Questions" link, and when the FAQ page comes up,
enter "timing chain" in the "Search Text" field and when the answers come
up, click on the "Timing Belt and Timing Chain" article. The results will
show that the 2002-2007 Camry 4 cylinder has a timing chain.
As far as whether or not there is a way to set cam timing, the way to set it
is to align the match marks on the camshafts and crankshaft before
installing the chain. Timing chain stretch should be negligible in a 5 year
old Camry, at least negligible enough to make checking the chain very low on
the list of possible causes of poor fuel economy.

The crankshaft and camshafts rotate. The variable valve timing feature on
the engine makes it difficult to determine when to ignite each spark plug,
so the ECU uses signals from the crankshaft and camshaft position sensors to
determine when to fire. Ignition timing is not adjustable as it is
controlled by the ECU. There is a spec for base ignition timing, but if it
is not within spec, then the check is to see if the crank and cam position
sensor gap is set correctly.

Ransley; it's time to leave the hay rack and threshing
machine behind.
This is modern times, the ECM computer gets a signal from
the crank position sensor and cam sensors and knows where
every rotating part is. It also reads manifold pressure,
throtle position, vehicle speed and sets the proper timing.
Slim

A change in size can throw off the odometer (it would take a major
change to reduce apparent mileage by 30%). A change in type can
increase rolling resistance (and decrease mileage, although not by
30%). Improper inflation of new tires can reduce mileage (but again,
probably not by 30%).
I doubt new and different tires could account for a 30% change in
apparent fuel economy, but it is a possibility. And just the act of
subjecting your car to a tire store could indicate a cause - like for
instance, while lifting your car to install the new tires they managed
to crimp an exhaust pipe (and increase back pressure), or they
"inspected" your brakes while installing new tires and managed to
screw something up so the brakes are dragging.
Something has changed. Asking about tires is one way of smoking out
what changed.
Ed

Changing the sensor behind the cat will have zero effect on mileage. The
rear sensor is not an input to the engine, its only used as a reference
for converter efficiency. Did you check tire pressure? Change gas stations
recently?

Your service station could have rigged the pumps to cheat you. Happened
in SoCal, about 100 stations in a chain. Pumps delivered accurate 5 and
10 gallon quantities so escaped the attention of inspectors. Any other
quantity, pump indicated and customer paid for quite a bit more gas than
he or she actually rec'd. Got away with it for two or three years, IIRC.

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